This size is the inner diameter measurement size:



The inside diameter of the XS shoes is 3.2cm long and 2.5cm wide



The inner diameter of S shoes is 3.8cm long and 2.8cm wide



The inside diameter of size M shoes is 4.3cm long and 3.2cm wide



The inner diameter of size L shoes is 4.8cm long and 3.5cm wide



XL shoes have an inner diameter of 5.4cm long and 4.0cm wide